The present invention relates to a system for providing pressurized fluid to a plurality of load circuits, and more particularly, to such a system in which one of the load circuits must be given "priority", i.e., the full flow demand of that primary circuit must be satisfied, with any excess flow available going to an auxiliary circuit.
Although the system of the present invention is equally adapted to any arrangement in which pressurized fluid is required for a primary load circuit and an auxiliary load circuit, its use is especially advantageous in arrangements in which the primary load circuit comprises a vehicle power steering system, and will be described in connection therewith.
It is known in the prior art to provide pressurized fluid to both a primary load circuit and an auxiliary load circuit by means of a single fluid pump and priority flow control valve. See U.S. Pat. No. 3,455,210, assigned to the assignee of the present invention. In view of the current concern over the efficient utilization of energy, one of the operating characteristics of such priority systems may represent a disadvantage. This characteristic is that when providing fluid to two different load circuits at substantially different load pressures (e.g., 1000 psi and 2000 psi), the priority valve must throttle the source pressure down to the lower load pressure, this throttling causing a substantial amount of the input energy to the pump to be converted to heat and wasted.
It is also known in the prior art to utilize one pump for the primary load circuit, and another pump for the auxiliary load circuit, with each of the pumps having sufficient capacity to satisfy the flow and pressure demands of its associated load circuit. This type of arrangement obviously results in unnecessary and expensive pump capacity.